This invention relates to improvements in methods and apparatus for elevating masses of fish and other articles with minimum damage employing a submersible rotary impeller-type pump as the primary pressure source. The invention is herein illustratively described by reference to the presently preferred form thereof; however, it will be recognized that certain modifications and changes with respect to details may be employed within the scope of the invention.
Lerch, U.S. Pat. Nos. 3,314,184 and 3,421,245, disclose significant advancements in the art of fish pumping, such as in brailing nets and in transferring fish from the holds of vessels to dockside or to other vessels. The portable compactness, operating reliability, high volumetric pumping capacity and versatility of rotary impeller submersible fish pump transfer systems disclosed in those patents gained early and widespread acceptance by the commercial fisheries of many countries. However, the incidents of flesh damage due to fish passing through the pump impeller has remained a serious limitation on the applicability of such systems, at least in some fisheries. For example, flesh damage of fish to be used in fishmeal plants causes significant loss of valuable proteins through leaching. The extent of flesh damage incurred becomes greater as pumping height is increased inasmuch as the pump rotor must be driven at correspondingly higher speeds, and larger and softer fish are naturally more vulnerable.
In one prior art effort to reduce flesh damage, a jet pump was used rather than a rotary impeller pump as the primary pumping device. That system utilized a suction hose with an inlet submersible in the water, with an air nozzle mounted at or near the inlet. A water jet pump mounted in the hose above the air injection nozzle directed its flow upwardly in the hose to induce flow upwardly to and above the jet.
A broad object of this invention is to greatly reduce, if not altogether overcome, the problem of damage as a material factor in commercial systems for pumping fish and other articles using a submersible rotary impeller pump as the primary pressure source. A related object is to permit pumping to the same or greater heights than were heretofore attainable with submersible rotary impeller pumps and with much less damage to the fish or other articles pumped.
A related further object is to devise such a system operable at any of wide-ranging submersion depths, and which indeed gains in operating efficiency and in reduction of flesh damage with increased operating depth.
It is also an object to achieve those advancements while retaining the described advantages of portable compactness, operating reliability, high volumetric capacity and versatility of use, and all without adding materially to the cost of the system.